Diaphragm for electric discharge tube



Feb 12, 1957 E. GOMONET 2,731,471

DIAPHRAGM FOR ELECTRIC mscmgcs TUBE Filed Sept. 27, 1955 Fig.

INVENTOR EDOUAR D GOMON ET ATTORNEYS:

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United States Patent DIAPHRAGM FOR ELECTRIC DISCHARGE TUBE Edouard Gomonet, Paris, France, assignor to Societe Anonyme pour les Applications de lElectricite et des I( laz Rares-Etablissements Claude-Paz & Silva, Paris,

rance Application September 27, 1955, Serial No. 536,852

Claims priority, application France September 28, 1954 2 Claims. (Cl. 313-174) The present invention relates to a diaphragm for application to an electric discharge tube having an atmosphere containing mercury vapour, said diaphragm being made of a material which is not wetted by clean mercury, and including at least one aperture through which liquid mercury cannot normally pass in both directions although it may pass from one side to the other of said diaphragm in one direction.

It is known to arrange, in the vicinity of an end of a discharge tube a diaphragm incorporating at least one aperture through which the mercury vapour may pass, but which cannot be traversed in both directions by liquid mercury under normal conditions, there being at least one direction in which, in only abnormal conditions will liquid mercury pass through the aperture. Such abnormal conditions may be brought about by a shake or movement of the tube of such strength and direction that liquid mercury will fall back through the aperture.

Such a diaphragm is utilized for preventing a reserve of liquid mercury from leaving a region which is favorable to its vaporization during the operation of a discharge tube including such a reserve. This vaporization offers the advantage that even with a relatively very low ambient temperature, the pressure of the mercury vapour is then sufficient for the emission of mercury radiations by the discharge to take place with a satisfactory efficiency in all regions through which the discharge passes.

The diaphragms proposed heretofore suffer from various disadvantages, for example diflicult or costly manufacturing or attaching of the diaphragm, head loss too high in the aperture during the pumping which takes place to effect removal of gases from the tube during manufacture.

The diaphragm according to the present invention does not offer such drawbacks. It is characterized in that the aperture formed therein is edged or bordered, on one side only of the diaphragm, by a rim formed by the whole, or by a part, of the material pressed out of the diaphragm in the formation of said aperture, said rim incorporating, at least in the zone adjacent that portion of the diaphragm surrounding the aperture, a plurality of breaks or interruptions which are sufiiciently narrow to prevent the passing of liquid mercury therethrough.

The diaphragm according to the invention may consist of a simple mica disc incorporating one or more apertures formed in the manner indicated above, such disc being adapted to be secured in the tube by softening the latter in the vicinity of the periphery of the disc. Such a diaphragm can easily be manufactured and fastened and its presence will result in little head losses for gases and vapours since the aperture or apertures may be as large as desired. It is a simple matter to ensure that the breaks in the rim will be sufiiciently narrow over the height of the rim the liquid mercury reaches when resting on the diaphragm, so that mercury will not flow through said breaks or interruptions.

For a better understanding of the invention and to show how the same may be carried into effect, one embodiment thereof will now be more fully described with reference to the accompanying drawings in which:

Figure 1 is an elevational view of one end of a discharge tube, such end incorporating a diaphragm.

Figure 2 is a plan view of the diaphragm used in Figure 1.

Figure 3 is a transverse section on a larger scale of the diaphragm and of the adjacent portion of the discharge tube in which it is mounted.

The electric discharge tube, one end of which is shown in Figure 1, is, for instance, a cold cathode fluorescent tube. The fluorescent coating does not reach the ends of tube 1, which makes it possible to see the electrode assembly 2 in the end of the tube.

' 4 denotes a diaphragm which is also shown separately in plan in Figure 2, such diaphragm being provided with an aperture 13 edged or bordered by a rim 6 obtained by pushing in, with a press, the central portion of the diaphragm. The diaphragm being made of mica, the rim 6 thus formed includes a number of breaks or interruptions such as 12, as shown in Figures 1 and 3. Since mercury does not wet the material of the diaphragm, it cannot go through narrow passage-ways, such as the breaks or interruptions in the rim, at least in that portion thereof closest to the body of the diaphragm.

. After it has been provided with the aperture 13 and with the rim 6, the diaphragm 4, the outer diameter of which is equal to or slightly less than the inner diameter of the tube 1, is fastened to one end of the tube in the following manner: the diaphragm is placed in the position it is to occupy whereafter heat is applied to the tube 1 until the glass of which the latter is made softens in the region of the periphery of the diaphragm; the softened glass tends to form an inwardly directed bulge in the wall of the tube, which bulge offers a groove in which the periphery of the diaphragm will be held. Figure 3, which is on a large scale, clearly illustrates this deformation of the glass.

Following the positioning and fastening of the diaphragm 4 the electrode 2 with its lead-in wires 7, 11 are then introduced into the electrode chamber of which Figure 1 shows the left hand portion, said electrode 2 and its associated lead-in wires 7, 11 being caused to pass through the aperture 13 in the diaphragm. The portion of the end of the tube 1 at the extreme left is then heated in a known manner until it softens, whereafter it is pressed so as to form a pinched portion 8 in which the wires 7 and 11 are sealed vacuum-tightly.

During the degassing and the filling of the tube 1, even when the exhaust tube of the discharge tube is placed in the pinched end portion 8, the aperture 13 allows a fairly easy passage of the gases which the vacuum pump is to remove from the tube, and subsequently of the gases with which the tube is filled. The mercury 5 from the reserve is easily placed in position by introducing it through an exhaust tube located, for instance, close to the electrode 2, and then tilting said tube. The formation of the rim 6 is such that it does not prevent the liquid mercury from passing from the right hand to the left hand side of the diaphragm through the aperture 13.

During later operations of manufacturing, transportation and placing in position of the tube 1, the mercury 5 will be unable to pass in a liquid condition towards the right hand side of the diaphragm since the rim 6 prevents it from going through the aperture 13 in that direction, and any spaces present between the periphery of the diaphragm and the glass of the tube are too fine for the liquid mercury to pass through. During the operation of the tube, the mercury 5 will be heated slightly (for instance by about 50 C.), by the electrode and Patented Feb. 12,1957

thevapour evolved willpass through the aperture 13 andwilhspread to a fairly. large distancefrom. the elec.-. trode, thus increasing the pressure of the mercury vapour in such a manner that, down to -10 C. for instance, the tube will give out nearly as much. lightatiallpoints provided with a fluorescent layer' and? thus will ofier' no: dark portions, except at the electrode chambers which. are generally hidden.

Figure 3 shows, on alarger scale, the diaphragm 4 and the adjacent portion of the tube I seen, inssection, the axis of that: end of the tube being vertical so that. the mercury 5 may contact the rim 6. This figure, also clearly shows the glass bulges 9, 101 in thegroovesxlS, 1'4of-- which the periphery of diaphragmAz ishoused.

In Figures 1, 2, 3, the rim-6 is generally of tapered form but it may also have a greaterconicity or, on the contrary, it may be nearly cylindricalror even flare out.- wardly towards the pinched end portion .8 of the tube.

Theaperture 13 maybe of a shape otherthancircular.

' For example, it may be-ofelongatedzor: polygonal shape.

The-diaphragm mayinclude several apertures, tone. at least of which is formed according .-tolthe invention, and possibly: one or more others which only leave narrow clearances so that liquid mercury cannot normally flow through them.

Suchadiaphragm, in theusual conditions of handling andtransportation, can hold a drop of several grams. of mercury, a suificient reserve for. ensuring a. uniform discharge for several thousand hours.

The diaphragm may be located at some other point in the tube. For example, it may be arranged. at the other side of the electrode, the latter being, insuch a case, like the reserve of mercury, placed between'the .end.o..the.--tube..and..thediaphragm.

What I claim is:

1. A diaphragm for an electric discharge tube having an atmosphere containing mercury vapor, said diaphragm being made of a material? notiwetted by clean mercury, and including at. least. one aperture. through which liquid mercury cannot normally flow in both'directions although it is possible; for; said mercury to; pass-from? one; side: of the: diaphragm to; the other: through. said, aperture said aperture being-formed: bypressing-out a. portion of the material of the diaphragm and being bordered; on-one sideonly, of thediaphragm, by arim for-medby at. least a part of the material pressed-out when forming the aperture, andi saidri'mi incorporating, at lea'stin: theazone adjacent that portion of, the.diaphrag m, which surrounds the aperture, a plurality of breaks which are sufficiently narrow to prevent the passing of liquid mercury therethrough.

2; An-electric discharge tubecomprising at leastoneelectrode, having an atmosphere containing-'mercury-va-- por-' and} a storeof liquid mercury which will be heated by said; electrode-- dnring 'theoperation of the tube, and comprising a-diaphragm according to claim 1, saiddiaphragm-being-secured to'the envelope of the tube in the vicinity of said electrode, the rim of the diaphragm being directed'towards that end ofthe-tube which'is closest to said'eIectrOde, and'liquid rnercury being located between said end andi the diaphragm.

No references cited. 

